Lovato seemed to disagree with the pop princess, telling the hopeful that while he had a "good voice", he needed to stand out from the crowd more.

The 19-year old is quoted as saying: "I think you just have to find out what makes you special and what separates you from all the other teenage boys in this industry."

She also went on to tease Cowell and L.A., apparently telling 52-year old Simon that he was "old and impatient" after he pressured her to make a decision on a contestant. Lovato is also said to have called him "grandpa" as they made their way into the auditions.

Reid later tweeted: "Day 1 @TheXFactorUSA and I have already been cut to shreds by @ddlovato. Let the games begin!"

Despite a few shaky moments, Cowell seemed pleased with his new panel, taking to Twitter to write: "One of the best audition days we have ever done."

[uuid=bdde4b17-6cd8-469f-9fd7-7353719f4c54]Paula AbdulNicole Scherzinger, with the second series of The X Factor USA due to return to Fox later this year.